Attractive Electrostatic Interactions Research Articles

Preparation of biomass carbon dots/carboxymethyl cellulose-based fluorescent hydrogel: Combines selective detection and visual adsorption for Copper(II)

Abstract In this study, we used nitrogen-doped carbon dots (NCDs), which were synthesized via the hydrothermal method of corn-stover biomass as raw material and polyethyleneimine (PEI) as the nitrogen source, introduced them into the carboxymethyl cellulose-based hydrogel to prepare an environmentally friendly fluorescent cellulose-based hydrogel (NCDs/CMC-PAM). NCDs/CMC-PAM was also used for simultaneous fluorescence monitoring and removal of Cu (II) in aqueous solution. The chemical and physical structures, adsorption behaviors and fluorescent properties of NCDs/CMC-PAM were investigated. The results showed that NCDs/CMC-PAM exhibited a well-linear response range of fluorescence response for Cu (II) (0∼100 μM, detection limit of 3.42 μM). NCDs/CMC-PAM showed maximum adsorption capacities of 237.71 mg/g for Cu (II), the adsorption process followed the Langmuir isotherm model and pseudo-second-order kinetic model, which is an exothermic spontaneous reaction with an increase in entropy. It can still maintain 79.03% of the original adsorption capacity after six cycles (pH=6). The adsorption mechanisms of NCDs/CMC-PAM for Cu (II) are intraparticle diffusion, electrostatic attraction, ion exchange, and ligand interaction. Hence, the present study provides a new green way to synthesize an adsorbent that can be applied for the adsorption and detection of heavy metal ions.

Influence of biochar on the removal of Microcystin-LR and Saxitoxin from aqueous solutions

The present study assessed the effective use of biochar for the adsorption of two potent HAB toxins namely, Microcystin-LR (MCLR) and Saxitoxin (STX) through a combination of dosage, kinetic, equilibrium, initial pH, and competitive adsorption experiments. The adsorption results suggest that biochar has excellent capabilities for removing MCLR and STX, with STX reporting higher adsorption capacities (622.53–3507.46 µg/g). STX removal required a minimal dosage of 0.02 g/L, while MCLR removal needed 0.4 g/L for > 90%. Similarly, a shorter contact time was required for STX removal compared to MCLR for > 90% of toxin removed from water. Initial pH study revealed that for MCLR acidic conditions favored higher uptake while STX favored basic conditions. Kinetic studies revealed that the Elovich model to be most suitable for both toxins, while STX also showed suitable fittings for Pseudo-First Order and Pseudo-Second Order in individual toxin systems. Similarly, for the Elovich model the most suited kinetic model for both toxins in presence of each other. Isotherm studies confirmed the Langmuir–Freundlich model as the best fit for both toxins. These results suggest adsorption mechanisms including pore filling, hydrogen bonding, π–π interactions, hydrophobic interactions, electrostatic attraction, and dispersive interactions.

Synthesis of weak cation exchange/C18 bifunctional magnetic polymers for pretreatment and determination of glufosinate and its two metabolites in plasma samples

This study focuses on the purification and detection of glufosinate (GLUF) and its metabolites N-acetyl GLUF and MPP in plasma samples. A Dikma Polyamino HILIC column was used for the effective retention and separation of GLUF and its metabolites, and the innovative addition of a low concentration of ammonium fluoride solution to the mobile phase effectively improved the detection sensitivity of the target analytes. Monodisperse core-shell weak cation exchange (WCX)/C18 bifunctional magnetic polymer composites (Fe3O4@WCX/C18) were prepared in a controllable manner, and their morphology and composition were fully characterized. The Fe3O4@WCX/C18 microspheres were used as a magnetic solid-phase extraction (MSPE) adsorbent for the sample purification and detection of GLUF and its metabolites in plasma samples combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The purification conditions of Fe3O4@WCX/C18 microspheres for GLUF and its metabolites in spiked plasma samples were optimized to achieve the best MSPE efficiency. The purification mechanisms of the target analytes in plasma samples include electrostatic attraction and hydrophobic interactions. Furthermore, the effect of the molar ratio of the two functional monomers 4-VBA and 1-octadecene in the adsorbent was optimized and it shows that the bifunctional components WCX/C18 have a synergistic effect on the determination of GLUF and its metabolites in plasma samples. In addition, the present study compared the purification performance of the Fe3O4@WCX/C18 microsphere-based MSPE method with that of the commercial Oasis WCX SPE method, and the results showed that the Fe3O4@WCX/C18 microsphere-based MSPE method established in this work had a stronger ability to remove matrix interferences. Under optimal purification conditions, the recoveries of GLUF and its metabolites in plasma were 87.6–111 % with relative standard deviations (RSDs) ranging from 0.2 % to 4.8 %. The limits of detection (LODs, S/N≥3) and limits of quantification (LOQs, S/N≥10) were 0.10–0.18 μg/L and 0.30–0.54 μg/L, respectively. The MSPE-LC-MS/MS method developed in this study is fast, simple, accurate and sensitive and can be used to confirm GLUF intoxication based not only on the detection of the GLUF prototype but also on the detection of its two metabolites.

In-silico investigation of mechanical behavior of hydrated Na-montmorillonite tactoid

Swelling clay minerals, exemplified by Na-montmorillonite (Na-Mt), are vital constituents in expansive soils and hold significant relevance in geotechnical engineering. Comprehending their distinctive swelling behavior upon hydration is imperative for managing potential damage to civil infrastructure. Conversely, this swelling property gives rise to numerous advantageous applications, including using these clays in barrier materials and nanocomposites. The hierarchical structure of montmorillonite, consisting of clay mineral layers, tactoids, aggregates, and assemblies of aggregates, plays a pivotal role in the swelling behavior of expansive clays. This investigation employs molecular dynamics (MD) and steered molecular dynamic (SMD) simulations to explore the nanomechanical properties of hydrated Na-Mt tactoids at various hydration levels. It provides insights into their responses to compression, tensile, and shear deformation. This study reveals increased hydration levels increase interlayer spacing in clay structures, resulting in higher average d‐values. Water molecules drive attractive electrostatic interactions with clay mineral layers, predominantly mediated by sodium ions, highlighting the complex interplay between interlayer hydration and tactoid stability. Higher hydration enhances tactoid compressibility, reducing the stress required for deformation by compressing water molecules and clay mineral layers in the interlayer space. The study also demonstrates a notable reduction in tensile modulus with increasing hydration, signifying the significant impact of even minimal hydration on interlayer cation-clay layer interactions. Hydrated tactoids exhibit altered mechanical responses in shear deformation compared to dry ones, requiring lower shear stress to detach the top clay layer from the tactoid. The presence of water molecules impedes the locking of clay mineral layers, further influencing mechanical properties. The results and insight provided by this work will contribute to a better understanding of the impact of interlayer hydration on the stability and response of swelling clay minerals.

Enhancing Phototoxicity in Human Colorectal Tumor Cells Through Nanoarchitectonics for Synergistic Photothermal and Photodynamic Therapies.

Phototherapies are promising for noninvasive treatment of aggressive tumors, especially when combining heat induction and oxidative processes. Herein, we show enhanced phototoxicity of gold shell-isolated nanorods conjugated with toluidine blue-O (AuSHINRs@TBO) against human colorectal tumor cells (Caco-2) with synergic effects of photothermal (PTT) and photodynamic therapies (PDT). Mitochondrial metabolic activity tests (MTT) performed on Caco-2 cell cultures indicated a photothermal effect from AuSHINRs owing to enhanced light absorption from the localized surface plasmon resonance (LSPR). The phototoxicity against Caco-2 cells was further increased with AuSHINRs@TBO where oxidative processes, such as hydroperoxidation, were also present, leading to a cell viability reduction from 85.5 to 39.0%. The molecular-level mechanisms responsible for these effects were investigated on bioinspired tumor membranes using Langmuir monolayers of Caco-2 lipid extract. Polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) revealed that the AuSHINRs@TBO incorporation is due to attractive electrostatic interactions with negatively charged groups of the Caco-2 lipid extract, resulting in the expansion of surface pressure isotherms. Upon irradiation, Caco-2 lipid extract monolayers containing AuSHINRs@TBO (1:1 v/v) exhibited ca. 1.0% increase in surface area. This is attributed to the generation of reactive oxygen species (ROS) and their interaction with Caco-2 lipid extract monolayers, leading to hydroperoxide formation. The oxidative effects are facilitated by AuSHINRs@TBO penetration into the polar groups of the extract, allowing oxidative reactions with carbon chain unsaturations. These mechanisms are consistent with findings from confocal fluorescence microscopy, where the Caco-2 plasma membrane was the primary site of the cell death induction process.

Efficient extraction of Au(Ⅲ) by a piperidine-based ionic liquid and exploration of the mechanism driving force

Efficient gold extraction is of paramount importance, but how to improve the extraction efficiency and enhance the driving force of the extraction process is still to be explored. This study introduces an innovative approach using versatility ionic liquids (ILs) to overcome existing challenges. A tailored IL was synthesized and employed computational tools, including the Interaction Region Indicator, to predict its effectiveness in gold extraction. Quantum chemical calculations elucidated the interplay between hydrogen bonding capability and ion exchange properties of the ILs. Subsequent optimization of experimental conditions (0.1 mol/L HCl, 10.6 mg IL) yielded a remarkable 98.4 % extraction efficiency at 45 °C. Molecular dynamics simulations affirmed the IL's exceptional selectivity for Au(III) extraction, with analysis revealing that the extraction mechanism primarily hinged on electrostatic attraction and van der Waals interactions between ionic liquid cations and [AuCl4]−. This mechanism aligns with the established anion exchange mechanism, validated through Ultraviolet–visible spectrometer (UV–Vis), Nuclear Magnetic Resonance spectrometer (NMR), and Liquid Chromatograph Mass Spectrometer (LC-MS) analyzes. To complete the extraction cycle, 1.0 mol/L K2C2O4 was employed as a stripping agent for efficient Au(III) recovery from the loaded IL phase, facilitating repeated extraction cycles. This study underscores the sustainability of the IL-based Au(III) extraction process, maintaining consistently high extraction rates even after five cycles. In summary, this method does not use solvent, enabling environmentally friendly Au(III) extraction.

Comparison of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS) removal in a combined adsorption and electrochemical oxidation process

This study focused on three of the most studied PFAS molecules, namely perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS). They were compared in terms of their adsorption capacity onto graphite intercalated compound (GIC), a low surface area, highly conductive and cheap adsorbent. The adsorption on GIC followed a pseudo second order kinetics and the maximum adsorption capacity using Langmuir was 53.9 μg/g for PFOS, 22.3 μg/g for PFOA and 0.985 μg/g for PFBS due to electrostatic attraction and hydrophobic interactions. GIC was added into an electrochemical oxidation reactor and >100 μg/L PFOS was found to be fully degraded (<10 ng/L) leaving degradation by-products such as PFHpS, PFHxS, PFPeS, PFBS, PFOA, PFHxA and PFBA below 100 ng/L after 5 cycles of adsorption onto GIC for 20 min followed by regeneration at 28 mA/cm2 for 10 min. PFBS was completely removed due to degradation by aqueous electrons on GIC flakes. Up to 98 % PFOA was removed by the process after 3 cycles of adsorption onto GIC for 20 min followed by regeneration at 25 mA/cm2 for 10 min. When PFBS was spiked individually, only 17 % was removed due to poor adsorption on GIC. There was a drop of 3–40 % by treating PFOS, PFOA and smaller sulfonates in a real water matrix under the same electrochemical conditions (20 mA/cm2), but PFOS and PFOA removal percentage were 95 and 68 % after 20 min at 20 mA/cm2.

A novel ionic liquid-entrapped MIL-101(Cr) framework with enhanced removal efficiency towards phosphate from aqueous solution.

Developing adsorbent materials with high adsorptive dephosphorization (ADP) is significant for treating phosphate from aqueous solutions and eutrophic water. Herein, the MIL-101(Cr) framework was entrapped ionic liquid (IL) of 1-butyl-3-methylimidazoliumbromide ionic liquid ([C4mem]+[Br]-) using a ship-in-a-bottle approach to obtain novel adsorbents [C4mem]+[Br]-@MIL-101(Cr) contained varied IL contents, namely C4mem@MIL-101. The characterization results revealed that the formed [C4mem]+[Br]- molecules interacted with the MIL-101(Cr) frameworks, enhanced their stability, and offered additional adsorption sites. The batch adsorptions of phosphate showed that the optimized C4mem@MIL-101 adsorbent loaded with ~ 7% IL-based N content had the highest phosphate absorbing capacity of ~ 200mg/g, outperforming the pristine MIL-101(Cr) and other adsorbents. The ADP efficiency was facilitated in the acidic media, where the phosphate ions of H2PO4- and HPO42- captured onto the C4mem@MIL-101 via several interactions, including electrostatic attraction, H-bonds, and chemical interactions. In the meantime, the coexisting anions diminished the phosphate adsorption because they competed with the pollutants at adsorption sites. Furthermore, phosphate treatment under the continuous fixed-bed conditions showed that 1g of the polyvinyl alcohol (PVA)-mixed C4mem@MIL-101 pellets purified 25l of water containing phosphate with a 1mg/l concentration. The results suggest that the novel [C4mem]+[Br]-@MIL-101(Cr) structure had a high potential for treating phosphate in aqueous solutions.

UV Irradiated SiO2 Nanoparticles as Insulin and Immunoglobulin Molecule Carriers

Abstract Insulin and immunoglobulin therapy is commonly administered through injections that are invasive and painful. They cannot be taken orally because digestive enzymes break them down. To protect against enzymes, drug molecules may be “packed”, which decreases interaction of the active surface of the molecule with the environment. Silica nanoparticles (SiO2) may be used to attach proteins like insulin or immunoglobulin for use in drug delivery. They are stable and biocompatible. Exposing SiO2 nanoparticles to UV radiation may control molecule–nanoparticle attachment because of their electrostatic interactions. This study demonstrates the influence of UV radiation of SiO2 nanoparticles on insulin and immunoglobulin molecule attachment. Alteration of the surface electric potential of SiO2 nanoparticles by UV radiation was determined using electron work function measurements. Influence of radiation on formation of molecule-nanoparticle complexes was assessed by spectrophotometry of their sedimentation rate in solution. Increasing UV exposure time negatively charges the surfaces of SiO2 nanoparticles. Insulin exhibits better adsorption with SiO2 nanoparticles compared to immunoglobulin, likely due to favourable conditions promoting attractive electrostatic interactions. Longer UV exposure weakens insulin adsorption but does not significantly affect immunoglobulin adsorption.

Triple Adaptation of Constitutional Dynamic Networks of Imines in Response to Micellar Agents: Internal Uptake-Interfacial Localization-Shape Transition.

Understanding the behavior of complex chemical reaction networks and how environmental conditions can modulate their organization as well as the associated outcomes may take advantage of the design of related artificial systems. Microenvironments with defined boundaries are of particular interest for their unique properties and prebiotic significance. Dynamic covalent libraries (DCvLs) and their underlying constitutional dynamic networks (CDNs) have been shown to be appropriate for studying adaptation to several processes, including compartmentalization. However, microcompartments (e.g., micelles) provide specific environments for the selective protection from interfering reactions such as hydrolysis and an enhanced chemical promiscuity due to the interface, governing different processes of network modulation. Different interactions between the micelles and the library constituents lead to dynamic sensing, resulting in different expressions of the network through pattern generation. The constituents integrated into the micelles are protected from hydrolysis and hence preferentially expressed in the network composition at the cost of constitutionally linked members. In the present work, micellar integration was observed for two processes: internal uptake based on hydrophobic forces and interfacial localization relying on attractive electrostatic interactions. The latter drives a complex triple adaptation of the network with feedback on the shape of the self-assembled entity. Our results demonstrate how microcompartments can enforce the expression of constituents of CDNs by reducing the hydrolysis of uptaken members, unravelling processes that govern the response of reactions networks. Such studies open the way toward using DCvLs and CDNs to understand the emergence of complexity within reaction networks by their interactions with microenvironments.

Dynamics of the Deformable Fluid Interface Interacting with an Approaching Solid under the Electrostatic Field.

A theoretical model was developed to describe the dynamics of a deformable fluid interface interacting with an approaching solid without contact by both the attractive electrostatic and van der Waals (i.e., vdW) interaction, analogous to the situation in the experiments by electric force microscopy (i.e., EFM) or electric-surface force apparatus (i.e., E-SFA) involved in the soft fluid interface. On the basis of this model, a numerical study of the deformation of the fluid interface, the force-vs-separation behavior, and the critical limiting conditions of contact has systematically been carried out. Our results show that the surface pressure induced by the electrostatic interaction plays a more prominent role in the deformation of the fluid interface than the vdW interaction does, and there exists a principal length scale associated with the relative strength of the electrostatic field to the surface tension, affecting the fluid interface shape under the electrostatic field. It was also shown that both the force-distance curves and the corresponding curves of fluid interface deformation peak versus distance for various electrostatic fields satisfy the universal scaling power law. Moreover, an analytical solution to the Euler-Lagrange differential equation governing the deformation of the fluid interface under the external electric field is obtained, and two extended formulas for explicitly describing the principal length scales that respectively characterize the lateral and longitudinal deformations of the fluid interface were determined.

Novel Defluorination Pathways of Perfluoroether Compounds (GenX): α-Fe2O3 Nanoparticle Layer Retains Higher Concentrations of Effective Hydrated Electrons.

The development of efficient defluorination technology is an important issue because the kind of emerging pollutant of hexafluoropropylene oxide dimer acid (GenX) as an alternative to perfluorooctanoic acid (PFOA) has the higher environmental risks. In the UV/bisulfite system, we first developed a hydrophobic confined α-Fe2O3 nanoparticle layer rich in oxygen vacancies, which accelerated the enrichment of HSO3- and GenX on the surface and pores through electrostatic attraction and hydrophobic interaction, retaining more hydrated electrons (eaq-) and rapidly destroying GenX under UV excitation. Especially, under anaerobic and aerobic conditions, the degradation percentage of GenX obtain nearly 100%, defluorination of GenX to 88 and 57% respectively. It was amazed to find that the three parallel H/F exchange pathways triggered by the rapid reactions of eaq- and GenX, which were unique to anaerobic conditions, improved the efficiency of fluoride removal and weaken the interference of dissolved oxygen and H+. Therefore, this study provided an available material and mechanism for sustainable fluoride removal from wastewater in aerobic and anaerobic conditions.

Polyamidoamine dendrimers modified MXene and its high-performance adsorption behavior for Cr(VI)

Heavy metal pollution of water is a worldwide problem. The enticing characteristics exhibited by transition metal carbides (MXene) render it a good choiceas an adsorbent for removal of water pollutants. However, the limited functional group diversity and number, as well as the inadequate stability of MXene, impose limitations on its suitability for the adsorption of specific target metal ions (e.g., Hexavalent Cr(VI)). Herein, polyamidoamine (PAMAM) dendrimers, namely hyperbranched surfactant polymers, are employed to modify MXene, enhancing its surface functional group diversity and number. The presence of abundant –NH2 groups on the surface of PAMAM-modified MXene greatly enhances the adsorption capacity for Cr(VI). The pseudo-second order kinetic model and Langmuir isotherm model are suitable for describing the adsorption process. According to the Langmuir isotherm model, the maximum adsorption capacity (qm) can reach approximately 318 mg·g−1. Additionally, this adsorbent also has an excellent adsorption selectability for Cr(VI) from coexistent cations solution. Through the mechanisms of electrostatic attraction, reduction, covalent bonds, and chelation interaction, the high-performance adsorption for Cr(VI) can be achieved. Notably, the presence of PAMAM polymer as a protector ensures good stability of the composite adsorbent throughout adsorption/desorption cycle. This work provides deep insights into the advancement of highly efficient MXene-based adsorbents for water purification applications.

Controlled synthesis of sulfhydryl-dendritic mesoporous silica nanospheres for ultrafast extraction and sensitive analysis of organochlorine herbicides containing amide groups

The distinctive morphology of dendritic mesoporous silica nanoparticles (DMSN) has recently attracted considerable attention in scientific community. However, synthesis of DMSN with well-defined structure and uniform size for ultrafast extraction of trace herbicide residues from environmental and food samples remains to be a compelling challenge. In this study, sulfhydryl functionalized dendritic mesoporous silica (SH-DMSN) was synthesized and the SH-DMSN showcases monodisperse microspheres with flower shape and precisely tailored and controllable pore sizes. This distinctive structural configuration accelerates mass transfer within the silica layer, resulting in heightened adsorption efficiencies. Furthermore, the particle sizes (455, 765, and 808) of the adsorbent can be meticulously fine-tuned by introducing distinct templates. Specifically, when the particle size is 765 nm, the optimized SH-DMSN exhibits a substantial specific surface area (691.32 m²/g), outstanding adsorption efficiencies (>90 %), remarkably swift adsorption and desorption kinetics (2 min and 3 min, respectively), and exceptional stability. The superior adsorption capabilities of this novel adsorbent, ranging from 481.65 to 1021.7 µg/g for organochlorine herbicides containing amide groups, can be attributed to the interplay of S-π interactions, halogen bonding, and electrostatic attraction interaction. These interactions involve the lone pair electrons of sulfhydryl and silanol groups with the π-electrons, halogen atoms and amide groups in herbicide molecules. This study not only offers a new perspective on advancing the practical utilization of dendritic mesoporous silica but also provides a pragmatic strategy for the separation and analysis of herbicides in diverse sample matrices.

COMPRESSION BETWEEN KAOLIN AND CORN SEED AS ADSORBENTS ON THE ADSORPTION OF METFORMIN HYDROCHLORIC FROM AQUEOUS SOLUTION UNDER DIFFERENT CONDITIONS

Metformin is currently the medicine used to treat hypoglycemia most frequently. We used kaolin and corn seed surfaces to draw out the drug metformin hydrochloride from aqueous solutions. The medicine metformin, which is currently the most frequently prescribed oral hypoglycemic, has outstanding safety profiles and is only contraindicated in people with definite medical problems, particularly chronic renal failure, congestive heart failure, chronic obstructive pulmonary disease, and liver disease. The analysis demonstrates how many factors, such as equilibrium time (5–15 min), pH (8.5) as well as for pH of small intestine, temperature (32–37°C). It is discovered that when temperature and pH increase, the amount of adsorbate present decreases, with equilibrium requiring 15 minutes. The wavelength used for the analysis of metformin HCl was (260 nm). To discover the appropriate adsorption parameters, it was chosen to apply response surface methodology (RSM). Through thorough physical characterization using techniques including FTIR it was demonstrated that the primary driving forces behind the adsorption processes are H-bonding, electrostatic attraction, and so-called (electron donor-acceptor) EDA interactions. Modeling revealed that the best explanation for the MF adsorption involved an isotherm that depended on Giles categorization, was spontaneous (ΔG = -5.9 kJ/mole), and was endothermic (ΔH = +12.14 kJ/mole).

Carrier capability of halloysite nanotubes for the intracellular delivery of antisense PNA targeting mRNA of neuroglobin gene

Peptide nucleic acid (PNA) is a DNA mimic that shows good stability against nucleases and proteases, forming strongly recognized complementary strands of DNA and RNA. However, due to its feeble ability to cross the cellular membrane, PNA activity and its targeting gene action is limited. Halloysite nanotubes (HNTs) are a natural and low-cost aluminosilicate clay. Because of their peculiar ability to cross cellular membrane, HNTs represent a valuable candidate for delivering genetic materials into cells. Herein, two differently charged 12-mer PNAs capable of recognizing as molecular target a 12-mer DNA molecule mimicking a purine-rich tract of neuroglobin were synthetized and loaded onto HNTs by electrostatic attraction interactions. After characterization, the kinetic release was also assessed in media mimicking physiological conditions. Resonance light scattering measurements assessed their ability to bind complementary single-stranded DNA. Furthermore, their intracellular delivery was assessed by confocal laser scanning microscopy on living MCF-7 cells incubated with fluorescence isothiocyanate (FITC)-PNA and HNTs labeled with a probe. The nanomaterials were found to cross cellular membrane and cell nuclei efficiently.Finally, it is worth mentioning that the HNTs/PNA can reduce the level of neuroglobin gene expression, as shown by reverse transcription-quantitative polymerase chain reaction and western blotting analysis.

The potential of ferrihydrite-synthetic humic-like acid composite as a soil amendment for metal-contaminated agricultural soil: Immobilization mechanisms by combining abiotic and biotic perspectives

In-situ passivation technique has attracted increasing attention for metal-contaminated agricultural soil remediation. However, metal immobilization mechanisms are mostly illustrated based on metal speciation changes and alterations in soil physicochemical properties from a macroscopic and abiotic perspective. In this study, a ferrihydrite-synthetic humic-like acid composite (FH-SHLA) was fabricated and applied as a passivator for a 90-day soil incubation. The heavy metals immobilization mechanisms of FH-SHLA were investigated by combining both abiotic and biotic perspectives. Effects of FH-SHLA application on soil micro-ecology were also evaluated. The results showed that the 5%FH-SHLA treatment significantly decreased the DTPA-extractable Pb, Cd and Zn by 80.75%, 46.82% and 63.63% after 90 days of incubation (P < 0.05), respectively. Besides, 5% FH-SHLA addition significantly increased soil pH, soil organic matter content and cation exchange capacity (P < 0.05). The SEM, FTIR, and XPS characterizations revealed that the abiotic metal immobilization mechanisms by FH-SHLA included surface complexation, precipitation, electrostatic attraction, and cation-π interactions. For biotic perspective, in-situ microorganisms synergistically participated in the immobilization process via sulfide precipitation and Fe mineral production. FH-SHLA significantly altered the diversity and composition of the soil microbial community, and enhanced the intensity and complexity of the microbial co-occurrence network. Both metal bioavailability and soil physiochemical parameters played a vital role in shaping microbial communities, while the former contributed more. Overall, this study provides new insight into the heavy metal passivation mechanism and demonstrates that FH-SHLA is a promising and environmentally friendly amendment for metal-contaminated soil remediation.

Highly selective recovery of palladium using innovative double-layer adsorptive membranes

Palladium (Pd) recovery from secondary resources is urgently needed to meet the rising demands for precious metals for sustainable development and environmental protection. To achieve the goal of simple, efficient, and selective recovery of precious metal Pd, we reported an innovative strategy that utilized a double-layer adsorptive membrane based on polydopamine (PDA) modification and polymethacryloxyethyltrimethyl ammonium chloride (PDMC) grafting. The adsorption results suggested that the adsorptive membrane exhibited an excellent adsorption capacity of 61.5 mg g−1 towards Pd(II) at pH 2.0 and the adsorption capacity remained stable after six cycles. Moreover, the adsorption processes of Pd(II) were fitted to pseudo second-order kinetic models and the Langmuir isotherm models. Density functional theory (DFT) simulation, and FTIR, XPS analysis indicated the adsorption mechanisms were ion exchange from the PDMC layer and chelation and ion exchange from the PDA layer. In the presence of other metal ions (Ni(II), Cu(II), Zn(II), Ca(II), Mg(II), K(I) and Na(I)), the separation factor of adsorptive membrane for Pd(II) was in the range of 50–529. The remarkable selectivity was due to the mechanism of the combination of electrostatic attraction and coordination interaction to Pd(II) while the electrostatic repulsion to other metal cations. Furthermore, membrane filtration results suggested that Pd(II) was effectively adsorbed and rejected and the leakage risk could be reduced by dual adsorption from the double-layer membrane. This study not only offers an innovative strategy to precisely and effectively recover Pd(II) and other platinum group metals, but also provides valuable insights for the future implementation of adsorptive membranes in recycling low-concentration wastewater in an efficient and friendly way.

A Kinetic Investigation of the Supramolecular Chiral Self-Assembling Process of Cationic Organometallic (2,2':6',2″-terpyridine)methylplatinum(II) Complexes with Poly(L-glutamic Acid).

The cationic platinum(II) organometallic complex [Pt(terpy)Me]+ (terpy = 2,2':6',2″-terpyridine) at mild acidic pH interacts with poly(L-glutamic acid) (L-PGA) in its α-helix conformation, affording chiral supramolecular adducts. Their kinetics of formation have been investigated in detail as a function of the concentrations of both reagents and changing pH, ionic strength, the length of the polymeric scaffold and temperature. After a very fast early stage, the kinetic traces have been analyzed as three consecutive steps, suggesting a mechanism based on the electrostatic fast formation of a not-organized aggregate that subsequently evolves through different rearrangements to form the eventual supramolecular adduct. A model for this species has been proposed based on (i) the attractive electrostatic interaction of the cationic platinum(II) complexes and the polyelectrolyte and (ii) the π-stacking interactions acting among the [Pt(terpy)Me]+ units.

Ligand coupling mechanism of the human serotonin transporter differentiates substrates from inhibitors

The presynaptic serotonin transporter (SERT) clears extracellular serotonin following vesicular release to ensure temporal and spatial regulation of serotonergic signalling and neurotransmitter homeostasis. Prescription drugs used to treat neurobehavioral disorders, including depression, anxiety, and obsessive-compulsive disorder, trap SERT by blocking the transport cycle. In contrast, illicit drugs of abuse like amphetamines reverse SERT directionality, causing serotonin efflux. Both processes result in increased extracellular serotonin levels. By combining molecular dynamics simulations with biochemical experiments and using a homologous series of serotonin analogues, we uncovered the coupling mechanism between the substrate and the transporter, which triggers the uptake of serotonin. Free energy analysis showed that only scaffold-bound substrates could initiate SERT occlusion through attractive long-range electrostatic interactions acting on the bundle domain. The associated spatial requirements define substrate and inhibitor properties, enabling additional possibilities for rational drug design approaches.